1. Field of the Invention
The invention relates to protection switching for transmission systems, and more particularly to application of protection switching for virtual private networks (VPNs).
2. Art Background
Network congestion control methods address the capacity of a network as a whole to carry the offered traffic. In contrast, flow control methods address the point-to-point communication between a sender and a receiver, by adapting the data rate of the sender to the data rate at which the receiver can process the traffic. Basically, congestion control methods address the ability of a network to handle traffic, while flow control addresses the ability of the receiving devices to follow the speed of the transmitting devices.
The majority of congestion control methods have traditionally been categorized as part of traffic management. Therefore, congestion control methods used in the past have involved methods that rely on modifying or shaping the traffic at the traffic source, or at the network entrance point, in order to prevent or to handle congestion. Typical congestion control techniques include “open loop” and “closed loop” methods. The open loop methods, by definition, involve steps the network takes prior to servicing the traffic. All open loop methods are based on pre-dimensioning the network and do not follow the dynamic changes in the traffic using the network.
Closed loop methods, on the other hand, are based on feedback received from the network. Closed loop techniques monitor the system to detect the time and location of congestion occurrence, convey the congestion notification to the parts of the system that can adjust the system operation, and ultimately, adjust the system operation. Closed loop methods are reactive in the sense that they do not act until congestion is already in place, and therefore service degradations may occur.
For the case of a fault in a transmission channel of the communication system—e.g., a channel failure which results in the loss of all data being transmitted via the channel, it is known to provide a protection channel for rerouting of the data from the channel experiencing the fault. The routing of traffic from a faulty channel onto the protection channel is known as protection switching.
Virtual Private Networks (VPNs) represent a class of transmission services for which congestion control has not been effectively developed. VPNs permit implementation of a private network through utilization of the public network infrastructure. Such networks may be implemented using technologies such as Internet Protocol (IP), Frame Relay, and Asynchronous Transfer Mode (ATM).
Accordingly, the need arises for protection switching of VPNs so that data can be reliably transmitted from source to destination at all times and especially during network failure. Additionally, the need arises for protection switching of VPNs so that network congestion can effectively be handled.